1. Field of the Invention
The present invention relates to an etching mask used for micromachining, a method of making the same, an etching method using the etching mask, a magnetic head device and a method of manufacturing the same, which are used for making writing poles and so on of a composite thin-film magnetic head device having a reading head and a writing head, for example.
2. Description of the Related Art
Demands have been increasing for techniques that achieve finer patterns as a reduction has been sought in size and film thickness of a magnetic head device such as a magnetoresistive (MR) head device used for a hard disk unit and various semiconductor devices. Fabrication of a micropattern includes an etching process. Anisotropic etching is required for achieving high etching accuracy in the etching process. Anisotropic etching has such orientation that a sidewall surface of a complete pattern is orthogonal to the surface of a base layer. An example that requires anisotropic etching is a composite thin-film magnetic head device having an inductive reading head and a magnetoresistive writing head. In order to achieve steady performance of the writing head of the magnetic head device, anisotropic etching is required to be performed orthogonally to the substrate for processing the writing pole (top pole) of the head.
As anisotropic etching, dry etching is preferred compared to wet etching achieved through a complete chemical reaction. Dry etching is to evaporate and remove an object, using reactive gas plasma or ion beams thereof. A photoresist is generally used as an etching mask for forming a pattern by dry etching.
One of problems found in such an etching process is that not only the workpiece to be etched but also the mask itself is etched. In the case of dry etching using ion beams, in particular, a photoresist mask is easily deformed since the etching speed of the mask by ion beams is high and the photoresist is sensitive to heat. The photoresist film may be made thick in order to prevent such deformation. However, an increased film thickness makes it difficult to maintain anisotropy of etching, which is not desirable for fine pattern fabrication.
To overcome the foregoing problem, a mask utilizing a metal such as copper (Cu) has been fabricated instead of a heat-sensitive photoresist film.
However, if a metal mask is used, a problem still remains, that is, the top and sidewall surface of the mask are removed together with the workpiece through an ion beam application although the etching speed of the mask is decreased. FIG. 14A to FIG. 14C illustrate such a state. As shown in FIG. 14A, a metal mask 101 is formed on a workpiece 100 and ion beam etching is performed. As shown in FIG. 14B and FIG. 14C, not only the surface of the workpiece 100 but also the top and sidewall surface of the metal mask 101 are removed by ion beams 102. As a result, a sidewall surface 101A of the patterned workpiece 100 is not perpendicular but has a cross section having the shape of a trapezoid whose top width is wider than the bottom width as shown in FIG. 14C. The interface between the sidewall surface 101A and the base layer takes a round shape.
In a composite thin film magnetic head device as mentioned above, in particular, if the cross section of a writing pole formed on a gap layer takes the shape of a trapezoid or the interface between the pole and the gap layer takes a round shape, leakage of magnetic flux results and affects data reading and writing. It is therefore desirable that the top surface of the writing pole layer is horizontal and sidewall surface is perpendicular, that is, the cross section is rectangular.
To achieve such a structure, a method is disclosed in Japanese Patent Application Laid-open Hei 3-252907 (1991) wherein a mask made of a metal (such as a nickel-iron alloy) whose etching speed is nearly similar to that of a workpiece is used. However, it is difficult to maintain sufficient anisotropy in this method, too, since the mask itself is removed through dry etching and part of the removed mask redeposits on the mask, and the mask thickness is required to be substantially thick (3 to 7 .mu.m) and so on.